Boil the potatoes with the skin on until soft, when cold to touch peel and prick them with a fork, then mix in a bowl with salt, 1/4 tsp of turmeric and 1/4 tsp of red chilli powder.
Heat up oil in a pan and shallow fry the potatoes until golden, then keep aside in a kitchen towel lined tray.
Blend the tomatoes into a pure.
Heat up 2 tbsp of mustard oil in a pan, add smashed green cardamom, 1 clove and 1 inch of cinnamon stick, roast the spices until aromatic then add the fennel and cumin seeds let them sizzle.
Add the Chopped onions, ginger and garlic and cook until raw garlic aroma disappears.
Add chopped green chilli cook for a few seconds, mix in the tomato puree, cook for 5 minutes then add the spices, turmeric, cumin, coriander and red chilli powder, season with salt and cook for 5 minutes more on medium flame.
Whisk the yoghurt in a bowl, reduce the flame add the yoghurt to the gravy mixing immediately, then add the peeled potatoes and a half cup of water, simmer for a few minutes.
Add garam masala powder and dried fenugreek leaves crushing them in your hand before mixing, cook for 2 minutes, add chopped fresh coriander and serve.